xep_0045: Require JID when setting outcast affiliation

Found out when reading poezio/poezio#3536.

“An admin or owner can ban one or more users from a room. The ban MUST
be performed based on the occupant's bare JID.”

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

slixmpp/plugins/xep_0045/muc.py

@@ -493,6 +493,8 @@ class XEP_0045(BasePlugin):
         """
         if affiliation not in AFFILIATIONS:
             raise ValueError('%s is not a valid affiliation' % affiliation)
+        if affiliation == 'outcast' and not jid:
+            raise ValueError('Outcast affiliation requires a using a jid')
         if not any((jid, nick)):
             raise ValueError('One of jid or nick must be set')
         iq = self.xmpp.make_iq_set(ito=room, ifrom=ifrom)